Locating the right parts

Sourcing parts for old systems can be a headache, but don’t be tempted by inexpensive replacements, warns Robin Kyte

Locating and sourcing a supplier of an obsolete mechanical component such as a bearing is a growing concern for many organisations, particularly if the component is part of a safety-critical system on an aircraft or nuclear power plant application.

Sourcing a bearing for a mechanical system on a military aircraft, for example, can be a challenging process, particularly if the system is an ageing one. The aircraft itself may have been in operational service for more than 40 years and may also be projected to remain in service for many more years to come.

However, if the operator needs to replace the original bearings there could be problems. the original supplier of the component may have ceased to exist, is now re-located overseas or perhaps is no longer willing to manufacture the equivalent bearing in small volumes of less than 1,000 units. This means that many aircraft and other mechanical system operators and managers are now facing significant bearing obsolescence issues, particularly if the quantity they require is relatively low.

There are similar issues in the nuclear industry. Bearings are commonly found in nuclear power plants as part of actuation systems, which position the control rods into the fuel bundle.

In an emergency situation, the rods are dropped into the fuel bundle to absorb the reactor heat, which dictates that the bearings must not fail under any circumstances. This means bearing suppliers must offer full manufacturing traceability, controlled lubrication and complete retention of records similar to the aerospace and defence industry.

The challenge for system operators is to find a bearing supplier that will manufacture the specified bearing to the same, or higher, quality standards as the original. They also need to find a manufacturer that is willing to supply in small batch sizes, which could range between 10 to 500 units.

In the case of high-risk applications such as those in the aerospace industry, bearings must be manufactured and controlled under the strict procedures mentioned above.

Often the bearing drawings on such legacy products will define only the chassis size, with little or no information regarding the internal design, materials or tolerances. With such a basic specification, a wide range of bearings could meet the requirements, ranging from low-precision, commercially-produced bearings to high-precision bearings with full traceability and inspection.

Some may be relatively inexpensive, but they were never designed to operate in these types of high-risk environments or applications. Often, the buyer does not realise that the bearing they have just purchased are not a like-for-like replacement. In order to avoid this scenario, customers should keep in mind three key issues: certification, full traceability and quality.

This can be ensured if customers visit the company’s manufacturing plant to witness the correct lubrication of a bearing. There are potential risks attached to fitting an incorrectly lubricated bearing for a nuclear or aircraft application, so customers can understand why it is beneficial to witness this process.

In the end they will probably pay more for custom bearings made in small batches, but they will likely have a much higher degree of quality compared with commercially-produced ones. The potential safety benefits of this justify any additional costs upfront.